This invention relates to an improvement in a process for making hydrogen peroxide by the cyclic anthraquinone process. More particularly, it relates to a process of regenerating activity of the platinum group metal catalyst used in said cyclic process.
Hydrogen peroxide is produced by a cyclic process in which an alkylanthraquinone dissolved in a water-immiscible solvent is hydrogenated in a reducing stage to produce the corresponding alkylanthrahydroquinone which is then oxidized to regenerate the alkylanthraquinone and to produce hydrogen peroxide. Hydrogen peroxide produced during oxidation is removed by extraction with water and the remaining solution which is called the working solution is recycled to the reduction stage. The hydrogenation is usually done in the presence of a catalyst in the form of a fixed bed or slurry. Due to various factors the catalyst undergoes a gradual reduction in activity which leads to excessive catalyst cost or time-consuming and expensive regeneration steps. Several methods of regenerating the catalyst without removal of it from the hydrogenation stage have been proposed.
British Patent Specification 1,348,071, published Mar. 13, 1974, discloses a method of reactivating the catalyst wherein the catalyst is regenerated in the hydrogenation stage during hydrogenation at full output by providing that the working solution coming from the extraction stage has a reactive hydrogen peroxide content of at least 250 mg. per liter of working solution. It is to be noted that in prior art methods, such as the above, regeneration is effected in the presence of hydrogen.
U.S. Pat. No. 3,004,831, issued to Hungerford et al. on Oct. 17, 1961, discloses a process for regenerating the hydrogenation catalyst used in an anthraquinone process by subjecting the catalyst in the hydrogenation stage to a periodic reduction in the hydrogen pressure, accompanied by introduction of inert gas. Hydrogenation itself must either be throttled to a considerable extent or stopped altogether during regeneration.
In spite of these proposed methods, there is still a need for improved methods of regenerating or maintaining activity of the catalyst used in the hydrogenation stage of a cyclic process for making hydrogen peroxide.